FIG. 1 schematically shows a typical onshore hydrocarbon well location and surface equipments SE above a hydrocarbon geological formation GF after some well-bore WB drilling operations have been carried out.
A first portion P1 of the well-bore is a cased portion. A casing string CS has been run into this first portion of the well-bore. Cementing operations have been carried out, in this first portion, for sealing the annulus CA (i.e. the space between the well-bore WB and the casing string CS). A second portion P2 of the well-bore is an open bore hole. A third portion P3 of the well-bore is a sensibly horizontal lateral bore hole. These various portions of the well-bore have various diameters.
Typically, the surface equipments SE comprise a plurality of mud tanks and mud pumps, a derrick, a drawworks, a rotary table, a power generation device and various auxiliary devices, etc. . . . A drill string DS couples the surface equipments with a drilling assembly DA. The drilling assembly comprises a drill bit DB. Typically, the drill string and the drilling assembly comprise an internal conduit through which a drilling fluid flow circulates.
After the first portion P1 of the well-bore has been drilled, the drilling assembly may be used to further drill the well-bore hole, for example the second portion P2 and/or the third portion P3. In addition, the drilling assembly may be move in and out of the well-bore hole in the event of failure of any part of the drilling assembly. Further, the drilling assembly when moved into the well-bore hole should be able to go through hole restrictions without being blocked.
Thus, there is a need to be able to adapt the diameter of the drilling bit DB1, DB2 and DB3 in order to pass through the various portions of the well-bore P1, P2 and P3, respectively.
The document WO01/81708 describes an expandable drill bit for use with earth drilling equipment. The bit includes arms held in a closed configuration, so that the bit may be inserted through casing or a small bore hole. The arms are expandable to create an expanded drill bit having a crown profile common to a solid crown bit. The arrangement of the arms provides a short gauge length so that the expanded bit is steerable downhole. The expandable drill bit comprises mechanisms for actuating the arms between the open and closed configurations. It appears that the expandable drill bit can be extended by using hydraulic force and/or latching mechanism. A limitation associated with this expandable drill bit is the need to control pressure or flow for activating the bit expansion/retraction. Another limitation associated with this expandable drill bit is that the shape of the bit is not adapted for use with low flow circulation. In case of low flow circulation (reverse or standard circulation), the fluid velocity may not be sufficient for cleaning the bit, resulting in failure due to cuttings getting stuck.